Many forms of data entry environments have been devised in the context of a symbolic grammar that defines valid data entry in various contexts. For example, in a data entry environment comprising a programming environment for the entry of a data set comprising a program, the symbolic grammar may specify, at any particular data entry position in the data set comprising the program, the symbols that a user may input that are syntactically valid, i.e., that can be validly parsed by the machine intended to execute the program. As another example, a hierarchical menu system may be devised for a telephone-base service, where the data set comprises the set of menu options that the user has selected to reach a particular location (i.e., a data entry position) in the hierarchical menu. Such a hierarchical menu system may consider the current menu position as a data entry position in the hierarchical menu, and may accept user input (e.g., a telephone button press and/or a spoken word) that corresponds to a selection among the menu options that are valid for that data entry position in the hierarchical menu system.